Since the first widespread use of thin-walled metal beverage cans, it has been the general practice to incorporate on one end of each can a self-contained opening means such as a pull tab connected to or cooperating with a tear flap with the pull tab arranged to be manually displaced to break open the tear flap and thereby release the contents from the can.
For example, in one of the most common early designs, the pull tab was connected directly to a tear flap designed to be pulled free of the can by manual operation of the annular pull tab to which the tear flap was attached. This configuration offered the user three poor alternatives; first, to discard immediately, usually on the ground, the detached tear flap and pull tab, the former with exposed raw metal edges, both unsightly and a serious hazard, especially in large quantities at beaches and other recreation facilities; second, to deposit the detached tear flap and pull tab inside the newly opened can before drinking the contents, a procedure creating a risk of ingesting the indigestible sharp edged tear flap with the contents of the can; and third, less likely, to hold on to the sharp edged tear flap and pull tab until the can is drained of its contents, and then deposit the tear flap and pull tab in the empty can for disposal therewith, with the possibility these loose parts inside will drop out of the can before it is deposited safely in a suitable trash receptacle.
More recently, the fully detachable tear flap and pull tab described above has been replaced by modified designs in which the pull tab is attached to the end of a can adjacent the tear flap and arranged to break open and rotate the tear flap inwardly of and still attached to a can to form an access opening therethrough, still presenting a raw metal edge relatively sharp and hazardous to someone using a can so equipped. Unfortunately, such "permanently attached pull tabs" usually made of thin sheet aluminum tend to remain sticking up from the end of the can adjacent the opening, so they are often torn loose with the same unfortunate alternatives described in the previous paragraph, often resulting in substantial quantities of undesirable pull tab discards underfoot, equally unsightly if less hazardous than the raw edged tear flaps. Even when such tabs are simply pushed back out of the way toward their initial ready position against the end of the can, they may break loose and depart unpredictably because the thin sheet aluminum of which they are usually made cracks very easily along the self-hinged portion of the pull tab.
An even more recent design configuration solved the problem of wayward pull tabs including those designed to remain permanently attached to the can, simply by eliminating the pull tab completely. Instead, a circular tear flap permanently attached to the can by a narrow self-hinged portion was rounded above the outer surface of the end of the can, to be broken open and displaced inwardly of the can to provide an access opening simply by the direct application of finger pressure to the rounded tear flap. Two serious problems remained. First, the exposed raw edge of the access opening posed a hazard to a user's finger pressed against the tear flap to open a can and a hazard to a user's lips placed against the access opening to drink from the can. Second the fully exposed and relatively raised tear flap, necessarily made relatively easy to break open by finger pressure, was too easily broken open by an accidental bump or blow during shipment and handling of large quantities of cans so fitted, or on display in stores by busy little fingers.